The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
An operating cycle of an internal combustion engine may include a plurality of engine strokes. For example, an operating cycle may include four different engine strokes. In an “intake stroke,” the engine may draw air into a cylinder through an intake manifold and one or more intake valves. The air may be mixed with fuel in the intake manifold (i.e. port fuel injection) or in the cylinder (i.e. direct fuel injection) to form an air/fuel (A/F) mixture. In a “compression stroke,” the A/F mixture may be compressed by a piston within the cylinder.
In a “power stroke,” the compressed A/F mixture may be combusted by a spark plug within the cylinder to drive the piston, rotatably turning a crankshaft to generate engine power. In an “exhaust stroke,” exhaust gas produced by the combustion of the A/F mixture (i.e. during the power stroke) may be expelled from the cylinder through an exhaust valve and an exhaust manifold.
The operating cycle may also be divided into an “expansion cycle” and a “non-expansion engine cycle.” More specifically, the non-expansion cycle may include the intake stroke and the exhaust stroke (i.e. the pumping strokes) and a first portion of the compression stroke. Alternatively, the expansion cycle may include a remaining portion of the compression stroke and the combustion stroke. In other words, the non-expansion cycle may include the engine strokes (or portions thereof) where negative work occurs (i.e. where heat is not released by combustion).
The combustion of the A/F mixture in the cylinder drives the piston, which applies a force on an engine crankshaft. The force on the engine crankshaft may be referred to as “combustion torque.” However, an amount of “drive torque” or “output torque” actually produced by the engine may be less than the combustion torque. More specifically, the drive torque may be less than combustion torque due to the energy losses (i.e. pumping losses) during the non-expansion engine cycle, engine friction, and/or additional loads on the engine from accessory devices (e.g. pumps, air conditioner, radio, etc.).